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Meta

Problems frequently reported at Meta, in course order. Solve the must-dos first.

37 easy99 medium20 hardIn-place linked-list rewiring ×11 Tree DFS (bottom-up) ×9 Stack for matching & nesting ×8 Two pointers (opposite ends) ×7 String parsing ×7 Tree BFS (level order) ×6

02 · Arrays & Strings in Java

#1672Richest Customer WealthEasy
#1431Kids With the Greatest Number of CandiesEasy

06 · Mindset & Problem Solving

#1480Running Sum of 1d ArrayEasy

07 · Big-O & Complexity

#69Sqrt(x)Easy

08 · Recursion

#24Swap Nodes in PairsMedium
#50Pow(x, n)Mediummust-do

09 · Math & Number Theory

#43Multiply StringsMediummust-do
#528Random Pick with WeightMediummust-do

10 · Arrays & Strings

#121Best Time to Buy and Sell StockEasymust-do
#31Next PermutationMediummust-do

11 · Matrices & Simulation

#48Rotate ImageMediummust-do
#73Set Matrix ZeroesMediummust-do

12 · Two Pointers

#125Valid PalindromeEasymust-do
#977Squares of a Sorted ArrayEasy
#167Two Sum II - Input Array Is SortedMediummust-do
#163Sum ClosestMedium
#26Remove Duplicates from Sorted ArrayEasy
#80Remove Duplicates from Sorted Array IIMedium
#283Move ZeroesEasy
#88Merge Sorted ArrayEasymust-do

13 · Sliding Window

#643Maximum Average Subarray IEasy
#424Longest Repeating Character ReplacementMediummust-do
#438Find All Anagrams in a StringMediummust-do
#76Minimum Window SubstringHardmust-do
#209Minimum Size Subarray SumMediummust-do
#1004Max Consecutive Ones IIIMediummust-do

14 · Hashing & Prefix Sums

#303Range Sum Query - ImmutableEasymust-do
#304Range Sum Query 2D - ImmutableMedium
#560Subarray Sum Equals KMediummust-do
#525Contiguous ArrayMedium
#974Subarray Sums Divisible by KMedium

15 · Linked Lists

#21Merge Two Sorted ListsEasymust-do
#141Linked List CycleEasymust-do
#234Palindrome Linked ListEasymust-do
#19Remove Nth Node From End of ListMediummust-do
#92Reverse Linked List IIMedium
#143Reorder ListMediummust-do
#2Add Two NumbersMediummust-do
#138Copy List with Random PointerMedium
#25Reverse Nodes in k-GroupHardmust-do

16 · Stacks & Monotonic Stack

#155Min StackMediummust-do
#150Evaluate Reverse Polish NotationMediummust-do
#739Daily TemperaturesMediummust-do
#84Largest Rectangle in HistogramHardmust-do
#394Decode StringMediummust-do
#71Simplify PathMedium
#32Longest Valid ParenthesesHard
#844Backspace String CompareEasy

17 · Queues & Deques

#232Implement Queue using StacksEasymust-do
#622Design Circular QueueMediummust-do
#239Sliding Window MaximumHardmust-do

18 · Binary Search

#34Find First and Last Position of Element in Sorted ArrayMediummust-do
#74Search a 2D MatrixMedium
#153Find Minimum in Rotated Sorted ArrayMediummust-do
#875Koko Eating BananasMediummust-do
#1011Capacity To Ship Packages Within D DaysMedium
#162Find Peak ElementMediummust-do
#278First Bad VersionEasymust-do
#658Find K Closest ElementsMedium

19 · Sorting

#148Sort ListMediummust-do
#274H-IndexMedium

20 · String Parsing & Expression Evaluation

#13Roman to IntegerEasymust-do
#151Reverse Words in a StringMediummust-do
#8String to Integer (atoi)Mediummust-do
#227Basic Calculator IIMediummust-do
#224Basic CalculatorHardmust-do
#271Encode and Decode StringsMediummust-do

21 · Tree Traversals

#94Binary Tree Inorder TraversalEasymust-do
#637Average of Levels in Binary TreeEasy
#199Binary Tree Right Side ViewMediummust-do
#103Binary Tree Zigzag Level Order TraversalMedium
#117Populating Next Right Pointers in Each Node IIMedium
#662Maximum Width of Binary TreeMedium
#863All Nodes Distance K in Binary TreeMediummust-do

22 · Tree Recursion

#110Balanced Binary TreeEasy
#100Same TreeEasy
#226Invert Binary TreeEasymust-do
#101Symmetric TreeEasymust-do
#572Subtree of Another TreeEasymust-do
#112Path SumEasy
#113Path Sum IIMediummust-do
#129Sum Root to Leaf NumbersMedium
#437Path Sum IIIMediummust-do
#543Diameter of Binary TreeEasymust-do
#124Binary Tree Maximum Path SumHardmust-do
#236Lowest Common Ancestor of a Binary TreeMediummust-do
#114Flatten Binary Tree to Linked ListMedium

23 · Binary Search Trees

#700Search in a Binary Search TreeEasy
#98Validate Binary Search TreeMediummust-do
#235Lowest Common Ancestor of a Binary Search TreeMediummust-do
#285Inorder Successor in BSTMediummust-do
#108Convert Sorted Array to Binary Search TreeEasy
#173Binary Search Tree IteratorMediummust-do

24 · Heaps & Priority Queues

#703Kth Largest Element in a StreamEasymust-do
#215Kth Largest Element in an ArrayMediummust-do
#347Top K Frequent ElementsMediummust-do
#973K Closest Points to OriginMediummust-do
#23Merge k Sorted ListsHardmust-do

25 · Tries

#208Implement Trie (Prefix Tree)Mediummust-do
#211Design Add and Search Words Data StructureMediummust-do
#1268Search Suggestions SystemMediummust-do

26 · Graphs: BFS & DFS

#695Max Area of IslandMediummust-do
#133Clone GraphMediummust-do
#54201 MatrixMediummust-do
#286Walls and GatesMedium
#785Is Graph Bipartite?Mediummust-do
#1091Shortest Path in Binary MatrixMediummust-do
#909Snakes and LaddersMedium
#1197Minimum Knight MovesMedium
#127Word LadderHardmust-do

27 · Shortest Paths

#787Cheapest Flights Within K StopsMediummust-do
#778Swim in Rising WaterHard
#1976Number of Ways to Arrive at DestinationMedium

28 · Union-Find & Minimum Spanning Trees

#547Number of ProvincesMediummust-do
#721Accounts MergeMediummust-do
#1489Find Critical and Pseudo-Critical Edges in Minimum Spanning TreeHard

29 · Topological Sort

#207Course ScheduleMediummust-do
#953Verifying an Alien DictionaryEasy
#269Alien DictionaryHardmust-do
#329Longest Increasing Path in a MatrixHardmust-do

30 · Advanced Graphs: Euler Paths, Bridges & SCCs

#332Reconstruct ItineraryHardmust-do
#1192Critical Connections in a NetworkHardmust-do
#399Evaluate DivisionMediummust-do

31 · Backtracking

#78SubsetsMediummust-do
#77CombinationsMediummust-do
#90Subsets IIMediummust-do
#46PermutationsMediummust-do
#40Combination Sum IIMedium
#17Letter Combinations of a Phone NumberMedium
#131Palindrome PartitioningMedium
#51N-QueensHardmust-do

32 · Greedy Algorithms

#55Jump GameMediummust-do
#763Partition LabelsMedium
#678Valid Parenthesis StringMediummust-do

33 · Intervals

#228Summary RangesEasy
#252Meeting RoomsEasy
#56Merge IntervalsMediummust-do
#57Insert IntervalMediummust-do
#435Non-overlapping IntervalsMediummust-do
#1094Car PoolingMedium

34 · Bit Manipulation

#268Missing NumberEasymust-do
#67Add BinaryEasymust-do
#371Sum of Two IntegersMedium

35 · Dynamic Programming

#91Decode WaysMediummust-do
#139Word BreakMediummust-do
#377Combination Sum IVMedium
#416Partition Equal Subset SumMediummust-do
#62Unique PathsMediummust-do
#1143Longest Common SubsequenceMediummust-do

36 · DP Patterns

#10Regular Expression MatchingHardmust-do
#647Palindromic SubstringsMediummust-do
#494Target SumMediummust-do

38 · Segment Trees, Fenwick & String Matching

#315Count of Smaller Numbers After SelfHardmust-do
#459Repeated Substring PatternEasy
#1392Longest Happy PrefixHardmust-do
#1044Longest Duplicate SubstringHard